In a disk drive, the adherence of a transducer to the surface of a disk with which it is in contact is a condition which is well known and is commonly referred to as "stiction". Various techniques have been proposed to avoid this condition and to deal with the condition when it exists. Efforts to eliminate the condition have included disk texturing, the application of a lubricant to a disk surface and the elimination of materials in the drive which exhibit outgassing contributing to the stiction condition. When the stiction condition exists, it is usually dealt with by applying brute force to separate the transducers and the disks, in a degree which does not damage the transducer suspension. If this does not free the disks for rotation, the disk drive is inoperative.
Such prior art techniques, other than brute force, usually produce uncertain results. The use of brute force, as practiced in the prior art, requires either disk spindle motors or transducer actuator motors of sufficient power to break the stiction bond. As the disk drives get smaller, the actuator motors are significantly reduced in power. In drives in the one-to-two inch form factor size range, actuator power is lacking for breaking stiction bonds.
Attention is therefore being directed to the disk spindle motor which drives the disk assembly or stack. Here also, however, in small drives, the motor is lacking in power to apply torque of sufficient magnitude, within the mechanical force limits of transducer suspensions, to break the stiction bond, using conventional motor starting techniques. In general, this also requires a torque constant (K) larger than is sometimes necessary or allowable for motor running speed requirements because of size requirements or restrictions. Winding resistance is increased because of the requirement for increased winding turns to produce the required torque. This is undesirable because of the increase in the electrical power requirement for normal operation. Moreover, in smaller disk drives, even with redesign as suggested, this brute force torque requirement may not be achievable.
One more recent teaching of a technique for breaking the stiction bond is described in U.S. Pat. No. 4,970,610, La Verne F. Knappe, inventor, entitled Magnetic Disk Drive Start Procedure For Starting Reaction Torque Amplification. Knappe addresses the problem using a brushless, direct current, three phase, delta wound disk spindle motor including Hall sensors. The motor is powered by coupling unidirectional direct current pulses thereto at a frequency which is stated to be the resonant frequency of the "stuck system". The stuck system includes the disk assembly, the actuator and any transducers that are stuck. A motion sensor is required to sense when the disk rotational motion is in the direction of desired rotation, the positive direction, to provide timing for the application of the unidirectional current pulses.